Method of preparing organo dialkylalkoxysilane

ABSTRACT

The invention relates to the preparation of organodialkylalkoxysilane using a continuous method consisting in bringing an alkanol into continuous contact with an omega-haloalkyl dialkylhalosilane in a countercurrent reactor, such as a plate column or a packed column. The reaction is performed in the aforementioned countercurrent reactor in the presence or absence of a non-reactive solvent with scavenging of the hydrochloric acid formed. The omega-haloalkyl dialkylalkoxysilane thus formed is particularly suitable for use as a starting material for the preparation of organosilicon compounds containing sulphur having general formula (I) by means of sulphidisation reaction on an alkaline metal polysulphide.

This application is an application under 35 U.S.C. Section 371 ofInternational Application Number PCT/FR2003/001921 filed on Jun. 23,2003.

The present invention relates to a process for preparing organodialkylalkoxysilane by a continuous process in the presence of analkanol on an omega-haloalkyl dialkylhalosilane.

The invention relates more particularly to the preparation of anethoxypropylsilane from a chloropropylsilane. Known processes on thissynthesis relate more specifically to dichloropropylsilane andtrichloropropylsilane. The process according to the invention allows3-chloropropyldimethylchlorosilane to be used as reactant, while givingethoxydimethyl-3-chloropropylsilane with very high yields. The chemicalreaction is as follows:ClMe₂Si—CH₂CH₂CH₂Cl+EtOH→(EtO)Me₂Si—CH₂CH₂CH₂Cl+HCl

The 3-chloropropyldimethylchlorosilane may be ethoxylated quantitativelyand selectively in the presence of a base. The use, for example, of anorganic base of tertiary amine type (including triethylamine) allows theacid formed to be neutralized stoichiometrically. However, the use of abase, and the lengthening and complication of the process that areassociated with its use and its eventual removal, constitute a certaindisadvantage. In the absence of base, moreover, the reaction leads toperformance levels which are unsatisfactory under conditionsconventionally used for this type of reaction: running ethanol into aninitial charge of 3-chloro-propyldimethylchlorosilane. This is a batchreactor process which gives excellent results only if the raw materialis dichloropropylmethylchlorosilane or trichloropropylchlorosilane:degree of conversion (DC)=100% and selectivity (RT)>95%. This is becausethe specificity of the dimethylchlorosilane moiety, compared for examplewith the trichlorosilane group, leads to a lower reactivity with respectto ethanol and, consequently, gives rise to more substantial formationof secondary products. These secondary products have come essentiallyfrom an oligomerization of the silane function, a reaction consecutiveto the following reaction:EtOH+HCl→EtCl+H₂O2[ClMe₂Si—CH₂CH₂CH₂Cl]+H₂O→ClCH₂CH₂CH₂—SiMe₂—O—Me₂Si—CH₂CH₂CH₂Cl+HCl

The principal aim of the present invention is specifically to provide ahigh-performance process, of the type above, whose starting product is amonochlorotriorganosilane, especially3-chloropropyldimethylchlorosilane, and which can be carried out in theabsence of base.

This aim, among others, is achieved by the present invention, whichrelates in effect to a process for preparing organodialkylalkoxysilaneby a continuous process which consists in contacting an alcohol, ofalkanol type for example, continuously in countercurrent with anomega-haloalkyldialkylhalo-silane.

The conversions obtained are generally greater than 90% and may reach100%, and the selectivities obtained are also very high.

The alcoholysis reaction deployed according to the invention may berepresented schematically by the following equation:

where:

-   -   the symbol Hal represents a halogen atom selected from chlorine,        bromine and iodine atoms, the chlorine atom being preferred,    -   the symbols R¹, which are identical or different, each represent        a monovalent hydrocarbon group selected from a linear or        branched alkyl radical having 1 to 15 carbon atoms and a linear        or branched alkoxyalkyl radical having 2 to 8 carbon atoms;    -   the symbols R² and R³, which are identical or different, each        represent a monovalent hydrocarbon group selected from a linear        or branched alkyl radical having 1 to 6 carbon atoms and a        phenyl radical;    -   A represents a removable group selected alternatively from: a        halogen atom Hal belonging to chlorine, bromine and iodine        atoms, the chlorine atom being preferred; or a radical        para-R⁰—C₆H₄—SO₂—O— where R⁰ is a linear or branched C1-C4 alkyl        radical, the tosylate radical para-CH₃—C₆H₄—SO₂—O— being        preferred; or a radical R⁰—SO₂—O— where R⁰ is as defined above,        the mesylate radical CH₃—SO₂—O— being preferred; or a radical        R⁰—CO—O— where R⁰ is as defined above, the acetate radical        CH₃—CO—O— being preferred, the most preferred radical A being        the chlorine atom.

According to the invention the continuous process therefore makes itpossible to carry out, in a countercurrent reactor, both thealkoxylation reaction and the separation of the stream of alkanol offormula (VIII) and of H-Hal (generally HCl) from the stream of silanes.Subsequently it is possible, if desired, finally to separate the alkanolfrom the H-Hal. Thereafter the alcohol thus purified can be reinjectedinto the reactor. More specifically the procedure is such that withinthe reactor a descending liquid fluid comprising the silane of formula(VII) and an ascending gaseous fluid comprising the alcohol of formula(VIII) will circulate in countercurrent. Also present within thereactor, in the vapor state, is the product of formula H-Hal.Advantageously the inside of the reactor in which the alcoholysisreaction is carried out is composed of a packed column or a plate columnso as to create reaction zones in liquid phase: the temperature isbetween the boiling temperature of the alcohol of formula (VIII) and theboiling temperature of the silane of formula (VII). The reaction iscarried out in the reactor alternatively at atmospheric pressure or atreduced pressure or at superatmospheric pressure.

In the advantageous implementation of the invention the alcohol isintroduced into the boiler and/or into the lower part of the column. Thesilane, for its part, is introduced at a location anywhere on the columnabove the zone where the alcohol is introduced. In this case the silanedescends the column in countercurrent and reacts in countercurrent withthe vaporized ethanol, which carries the HCl formed to a condensersituated at the top of the column, or else the mixture in the vaporstate is separated elsewhere. The alkoxylated silane is recovered at thebottom of the column, in the boiler, and/or is taken off at the side inthe lower part of the column.

The process comprises the stripping or vapor entrainment of the HClformed from the reaction mixture and the shifting of the equilibrium byincreasing the concentration of alkanol (ethanol) by distilling ethanolfrom the reaction mixture in order to remove HCl.

It is preferable, so as always to have an excess of alcohol, to operatethe reactor by working with an alcohol/silane molar ratio of greaterthan 1 and, preferably, between 1.2 and 20. In the case of theethanol/3-chloropropyldimethylchlorosilane pairing, this alcohol/silanemolar ratio is greater than 1.2 and preferably greater than 3, andgenerally is at most 20.

It is preferable, moreover, in the advantageous implementation of theinvention, to introduce the alcohol in the lower part of the column andthe silane in the upper part of the column.

The column may be equipped in its internal structure with dumped orordered packing or else with plates. Controlling the reflux rate is anadvantageous means for adjusting the profile of temperatures in thecolumn, but particularly for regulating the amount of H-Hal present inthe column.

One operational improvement of this countercurrent reactor may consistin at least one side removal of the gaseous streams based on alcohol andon H-Hal at one or more locations of the column, in order to minimizethe concentration of Hal in the reactor. It is known that H-Hal which isnot removed can limit the shifting of the reaction at equilibrium andmay give rise to parasitic reactions. A fresh alcohol stream or a streamresulting from recycling of the acidic alcohol may be injected into eachremoval zone in order to compensate the fluid removed.

As indicated above, in the case where the products corresponding toformulae (VII), (VIII) and (IX) have ethyl groups R¹ and methyl groupsR² and R³ and A and Hal represent a chlorine atom, the alcohol is analcohol constituted by ethanol and the silane is3-chloropropyldimethylchlorosilane, with formation of HCl.

If the reaction is conducted at atmospheric pressure the reactiontemperature within the reactor, and in particular within the column,must be greater than that of the stripping carrier gas, i.e., forexample, 78° C. in the case of ethanol, and less than the temperature ofthe 3-chloropropyldimethylchlorosilane, i.e., 178° C. It is thereforerecommended to operate at reduced pressure in order to limit thesolubility of HCl in the ethanol and to conduct the reaction at atemperature less than that corresponding to one atmospheric pressure,which allows the parasitic reactions to be limited and selectivity gainsto be made.

The acidic alcohol, in other words the alcohol laden with HCl, must bepurified before being recycled into the reaction mixture, bydistillation, azeotropic distillation where appropriate, by adsorptionon resin, by neutralization or by membrane separation.

The stripping of the HCl may be coupled with a stripping of the waterpresent in the mixture, by operating at a temperature greater than theboiling temperature of water at the pressure in question.

The alcoholysis reaction in this countercurrent reactor may be carriedout optionally in the presence of an organic solvent and/or an inertgas. The solvent is aprotic and relatively nonpolar, such as aliphaticand/or aromatic hydrocarbons. The solvent used has a boiling temperatureat the service pressure (atmospheric pressure) of between the boilingtemperature of the alcohol of formula (VIII), for example 77.8° C. forethanol, and that of the silane of formula (VII), for example 178° C.for 3-chloropropyldimethylchlorosilane. As an appropriate solvent forthe ethanol/3-chloropropyldimethylchlorosilane pairing mention may bemade in particular of toluene, monochlorobenzene and xylene. Thefunction of the solvent is to strip the hydrochloric acid (HCl) bymechanical entrainment (the alcohol is also entrained, and recyclingafter purification may be contemplated) and also to create a depletionzone (no HCl, or very little, at the bottom of the column) in order tominimize the parasitic chemical reactions.

The organodialkylalkoxysilane of formula (IX) thus obtained can be usedmore particularly as a starting product for preparing organosiliconcompounds containing sulfur, of the general average formula (I):

in which:x is an integral or fractional number ranging from 1.5±0.1 to 5±0.1; andthe symbols R¹, R², R³, Hal and A are as defined above.

In the formula (I) above, the preferred radicals R¹ are selected fromthe following radicals: methyl, ethyl, n-propyl, isopropyl, n-butyl,CH₃OCH₂—, CH₃OCH₂CH₂— and CH₃OCH(CH₃)CH₂—; more preferably the radicalsR¹ are selected from the following radicals: methyl, ethyl, n-propyl andisopropyl.

The preferred radicals R² and R³ are selected from the followingradicals: methyl, ethyl, n-propyl, isopropyl, n-butyl, n-hexyl andphenyl; more preferably the radicals R² and R³ are methyls.

The integral or fractional number x ranges preferably from 3±0.1 to5±0.1 and more preferably from 3.5±0.1 to 4.5±0.1.

The polysulfur monoorganoxysilanes corresponding to the formula (I)which are a specific objective of the present invention are those offormula:

in which the symbol x is an integral or fractional number ranging from1.5±0.1 to 5±0.1, preferably from 3±0.1 to 5±0.1 and more preferablyfrom 3.5±0.1 to 4.5±0.1.

In the present specification it will be specified that the symbol x inthe formulae (I), (II), (III) and (IV) is an integral fractional numberrepresenting the number of sulfur atoms present in one molecule offormula (I), (II), (III) and (IV).

In practice this number is the average of the number of sulfur atoms permolecule of compound under consideration, insofar as the selectedsynthesis route gives rise to a mixture of polysulfur products eachhaving a different number of sulfur atoms. The polysulfurmonoorganoxysilanes synthesized are in fact composed of a distributionof polysulfides, ranging from the monosulfide to heavier polysulfides(such as S_(≧5), for example) centered on an average molar value (valueof the symbol x) which is situated within the general ranges

(x ranging from 1.5±0.1 to 5±0.1), preferentially (x ranging from 3±0.1to 5±0.1) and more preferentially (x ranging from 3.5±0.1 to 4.5±0.1)mentioned above.

The products of formula (I) may be prepared as follows from theorganodialkylalkoxysilane of formula (IX) prepared beforehand in thecourse of step b) by the continuous process of the invention, byreacting said product of formula (IX) in the course of step c) with analkali metal polysulfide of formula (X) in accordance with the followingreaction scheme: step c):

where:

-   -   the symbols R¹, R², R³, A and x are as defined above,    -   the symbol M represents an alkali metal,    -   the reaction is carried out:        -   by reacting, at a temperature ranging from 20° C. to 120°            C., either the reaction mixture obtained at the end of step            (b), or the monoorganoxydiorganosilyl-propyl derivative of            formula (IX), taken in isolation after separation from said            reaction mixture, with the metal polysulfide of formula (X)            in the anhydrous state, using 0.5±15 mol % of metal            polysulfide of formula (X) per mole of the reactant of            formula (IX) and optionally operating in the presence of an            inert polar (or nonpolar) organic solvent,        -   and by isolating the bis(monoorganoxysilylpropyl)            polysulfide of formula (I) that is formed.

The continuous process according to the present invention allows accessto bis(monoorganoxysilylpropyl) polysulfides of formula (I). Thediorganohalosilanes of formula (VII) can be prepared advantageously onthe industrial scale by a process such as, in particular, that describedin WO-A-99/31111, cited as reference.

The process according to the invention for preparing products of formula(I) proceeds virtually quantitatively, without employing reactantsand/or without forming secondary products which are toxic compounds orpollutants to the environment (such as H₂S and alkali metals in the caseof the polysulfiding step).

The starting product in step b) of formula (VII) can be preparedaccording to the following process: step a)

where:

-   -   the symbol Hal represents a halogen atom selected from chlorine,        bromine and iodine atoms, the chlorine atom being preferred, and    -   the symbols A, R² and R³ are as defined above,        the reaction being carried out:    -   by reacting, at a temperature ranging from −10° C. to 200° C.,        one mole of the diorganohalosilane of formula (V) with a molar        amount which is stoichiometric or different from the        stoichiometry of the allyl derivative of formula (VI), the        operation being carried out in a homogeneous or heterogeneous        medium in the presence of an initiator consisting:        -   either of a catalytic activator consisting of:            -   (i) at least one catalyst comprising at least one                transition metal or one derivative of said metal, taken                from the group consisting of Co, Ru, Rh, Pd, Ir and Pt;                and optionally (2i) at least one hydrosilylation                reaction promoter,        -   or of a photochemical activator, consisting in particular of            appropriate ultraviolet radiation or appropriate ionizing            radiation,            and optionally by isolating the diorganohalosilylpropyl            derivative of formula (VII) that is formed.

According to one particularly suitable embodiment of the invention theprocess which has just been described consists in linking together steps(a), (b) and (c) in the definition of which the products of formulae(I), (V), (VI), (VII), (VIII) and (IX) have ethyl groups R¹ and methylgroups R² and R³ and the removable group A corresponds to the symbol Halrepresenting a halogen atom selected from chlorine, bromine and iodineatoms, and, preferably, a chlorine atom.

Step (a) consists in reacting the diorganohalosilane of formula (V) withthe allyl derivative of formula (VI) in the presence of a selectedinitiator. The initiator used embraces all of the initiators,corresponding to the types indicated above, which are effective inactivating the reaction between a ≡SiH function and an ethylenicunsaturation.

According to one preferred arrangement concerning the initiator, thelatter is selected from catalytic activators. These catalytic activatorscomprise:

-   -   as the catalyst (or catalysts), (i): (i-1) at least one finely        divided elemental transition metal; and/or (i-2) a colloid of at        least one transition metal; and/or (i-3) an oxide of at least        one transition metal; and/or (i-4) a salt derived from at least        one transition metal and a mineral or carboxylic acid; and/or        (i-5) a complex of at least one transition metal equipped with        organic ligand(s) which may possess one or more heteroatoms        and/or organosilicon ligands; and/or (i-6) a salt as defined        above in which the metal moiety is equipped with ligand(s) as        also defined above; and/or (i-7) a metal species selected from        the aforementioned species (elemental transition metal, oxide,        salt, complex, complexed salt) where the transition metal is        combined this time with at least one other metal selected from        the class of the elements of groups 1b, 2b, 3a, 3b, 4a, 4b, 5a,        5b, 6b, 7b and 8 (with the exception of Co, Ru, Rh, Pd, Ir and        Pt) of the Periodic Table as published in “Chemistry and        Physics, 65^(th) edition, 1984-1985, CRC Press, Inc.”, said        other metal being taken in its elemental form or in a molecular        form, it being possible for said combination to give rise to a        bimetallic or polymetallic species; and/or (i-8) a metal species        selected from the aforementioned species (elemental transition        metal and transition metal/other metal combination; oxide, salt,        complex and complexed salt on a transition metal base or on a        transition metal/other metal combination base which is supported        on an inert solid support such as alumina, silica, carbon black,        a clay, titanium oxide, an aluminosilicate, a mixture of        aluminum and zirconium oxides, or a polymer resin;    -   as the optional promoter (or promoters) (2i): a compound, which        may take for example the form of a ligand or of an ionic        compound, taken in particular from the group consisting of: an        organic peroxide; a carboxylic acid; a carboxylic salt; a        tertiary phosphine; an amine; an amide; a linear or cyclic        ketone; a trialkylhydrosilane; benzothiazole; phenothiazine; a        trivalent metal —(C₆H₅)₃ compound where metal=As, Sb or P; a        mixture of amine or of cyclohexanone with an organosilicon        compound containing one or more —Si≡H groups; the compounds        CH₂═CH—CH₂—OH or CH₂═CH—CH₂—OCOCH₃; a lactone; a mixture of        cyclohexanone with triphenylphosphine; an ionic compound such as        for example a nitrate or a borate of an alkali metal or of        imidazolinium, a phosphonium halide, a quaternary ammonium        halide or a tin(II) halide.

According to one more preferred arrangement concerning the initiator,the latter is selected from the preferred catalytic activators mentionedabove which comprise, as the catalyst (or catalysts) (i), one and/orother of the metallic species (i-1) to (i-8) where the transition metalbelongs to the following subgroup: Ir and Pt.

According to one even more preferred arrangement concerning theinitiator, the latter is selected from the preferred catalyticactivators mentioned above which comprise, as the catalyst (orcatalysts) (i), one and/or other of the metallic species (i-1) to (i-8)where the transition metal is Ir. In the context of this even morepreferred arrangement, suitable Ir-based catalysts are especially:

-   -   [IrCl(CO) (PPh₃)₂]    -   [Ir (CO)H(PPh₃)₃]    -   [Ir(C₈H₁₂) (C₅H₅N)P(C₆H₁₁)₃]PF₆    -   [IrCl₃],nH₂O    -   H₂[IrCl₆],nH₂O    -   (NH₄)₂IrCl₆    -   Na₂IrCl6    -   K₂IrCl₆    -   KIr(NO)Cl₅    -   [Ir (C₈H₁₂)₂]⁺BF₄ ⁻    -   [IrCl (CO)₃]_(n)    -   H₂IrCl₆    -   Ir₄(CO)₁₂    -   Ir(CO)₂(CH₃COCHCOCH₃)    -   Ir(CH₃COCHCOCH₃)    -   IrBr₃    -   IrCl₃    -   IrCl₄    -   IrO₂    -   (C₆H₇) (C₈H₁₂) Ir.

In the context of the even more preferred arrangement mentioned above,other Ir-based catalysts which are even more suitable are taken from thegroup of the iridium complexes of formula:[Ir(R⁴)Hal]₂  (XI)where:

-   -   the symbol R⁴ represents a conjugated or nonconjugated, linear        or cyclic (mono- or polycyclic) polyene ligand having 4 to 22        carbon atoms and from 2 to 4 ethylenic double bonds;    -   the symbol Hal is as defined above.

As an example of iridium complexes of formula (XII) which are even moresuitable mention will be made of those in whose formula:

-   -   the symbol R⁴ is selected from 1,3-butadiene, 1,3-hexadiene,        1,3-cyclohexadiene, 1,3-cyclooctadiene, 1,5-cyclooctadiene,        1,5,9-cyclododecatriene and norbornadiene and    -   the symbol Hal represents a chlorine atom.

As specific examples of iridium complexes which are even more suitablemention will be made of the following catalysts:

-   -   di-μ-chlorobis(η-1,5-hexadiene)diiridium,    -   di-μ-bromobis(η-1,5-hexadiene)diiridium,    -   di-μ-iodobis(η-1,5-hexadiene)diiridium,    -   di-μ-chlorobis(η-1,5-cyclooctadiene)diiridium,    -   di-μ-bromobis(η-1,5-cyclooctadiene)diiridium,    -   di-μ-iodobis(η-1,5-cyclooctadiene)diiridium,    -   di-μ-chlorobis(η-2,5-norbornadiene)diiridium,    -   di-μ-bromobis(η-2,5-norbornadiene)diiridium,    -   di-μ-iodobis(η-2,5-norbornadiene)diiridium.

The catalyst may be used—and this is another preferential arrangement—ina homogeneous medium, as described in JP-B-2 938 731. In this contextthe reaction may be conducted continuously, semicontinuously orbatchwise. At the end of operation the product of the reaction isseparated and collected by distillation of the reaction mixture, and thecatalyst can be recycled by producing a new charge of reactants on adistillation residue containing the catalyst from the distillation stepof the product of the preceding operation, with complementary additionof new catalyst where appropriate. Where complexes are employed therecycling of the catalyst can be enhanced by further adding a smallamount of ligand.

The catalyst may also be used in heterogeneous medium. This operatingmethod has recourse in particular to the employment of a catalyst whichis supported on an inert solid support of the type of those definedabove. This operating method makes it possible to carry out the reactionin a fixed-bed reactor operating continuously, semicontinuously orbatchwise with recycling. It is also possible to carry out the reactionin a standard stirred reactor operating continuously, semicontinuouslyor batchwise.

As far as the other reaction conditions are concerned, the reaction iscarried out within a wide range of temperatures, ranging preferably from−10° C. to 100° C., under atmospheric pressure or under a pressuregreater than atmospheric pressure, which may reach or even exceed 20×10⁵Pa.

The amount of the allyl derivative of formula (VI) used is preferablyfrom 1 to 2 mol per mole of organosilicon compound. As for the amount ofcatalyst(s) (i), expressed by weight of transition metal taken from thegroup consisting of Co, Ru, Rh, Pd, Ir and Pt, it is situated within theinterval ranging from 1 to 10 000 ppm, preferably ranging from 10 to2000 ppm and more preferably ranging from 50 to 1000 ppm, these figuresbeing based on the weight of organosilicon compound of formula (V) or(IX). The amount of promoter(s) (2i), when one or more promoters areused, expressed in numbers of moles of promoter(s) per gram-atom oftransition metal taken from the group consisting of Co, Ru, Rh, Pd, Irand Pt, is situated in the interval ranging from 0.1 to 1000, preferablyranging from 0.5 to 500 and more preferably ranging from 1 to 300. Thediorganohalosilylpropyl derivative of formula (VII) is obtained with amolar yield of at least 80%, based on the starting organosiliconcompound of formula (V).

According to one preferred arrangement the anhydrous metal polysulfidesof formula (X) are prepared by reacting an alkali metal sulfide,optionally containing water of crystallization, of formula M₂S (XII), inwhich the symbol M has the meaning given above (alkali metal), withelemental sulfur, operating at a temperature ranging from 60° C. to 300°C., optionally under pressure and also optionally in the presence of ananhydrous organic solvent.

Advantageously the alkali metal sulfide M₂S employed is the industriallyavailable compound, which is generally in the form of a sulfide hydrate:one alkali metal sulfide of this type which is highly suitable is theNa₂S sulfide available commercially, which is a hydrated sulfidecontaining 55 to 65% by weight of Na₂S.

According to a more preferred arrangement for conducting step (c) theanhydrous metal polysulfides of formula (X) are prepared beforehand froman alkali metal sulfide M₂S in the form of a hydrated sulfide, accordingto a procedure which consists in linking together the followingoperating phases (1) and (2):

-   -   phase (1), where the alkali metal sulfide hydrate is dehydrated        by applying the appropriate method which makes it possible to        remove the water of crystallization while retaining the alkali        metal sulfide in the solid state throughout the dehydration        phase;    -   phase (2), where subsequently one mole of dehydrated alkali        metal sulfide obtained is contacted with n(x-1) moles of        elemental sulfur, the operation being carried out at a        temperature ranging from 20° C. to 120° C., optionally under        pressure and optionally again in the presence of an anhydrous        organic solvent, the aforementioned factor n being situated        within the range from 0.8 to 1.2 and the symbol x being as        defined above.

With regard to phase (1), as a highly suitable dehydration protocolmention will be made in particular of the drying of the hydrated alkalimetal sulfide, operating under a partial vacuum ranging from 1.33×10² Pato 40×10² Pa and bringing the compound to be dried to a temperatureranging, at the beginning of drying, from 70° C. to 85° C., then bygradually raising the temperature in the course of drying from the zoneranging from 70° C. to 85° C. until it reaches the zone ranging from125° C. to 135° C., in accordance with a program which envisages a firsttemperature rise of +10° C. to +15° C. after a first period varying from1 hour to 6 hours, followed by a second temperature rise of +20° C. to+50° C. after a second period varying from 1 hour to 4 hours.

With regard to phase (2), as a highly suitable sulfiding protocolmention will be made of the implementation of this reaction in thepresence of an anhydrous organic solvent; appropriate solvents are, inparticular, lower (C1-C4) aliphatic alcohols which are anhydrous, suchas anhydrous methanol or ethanol, for example. The number of atoms ofelemental sulfur S_(x) in the metal polysulfide M₂S_(x) is a function ofthe molar ratio of S with respect to M₂S; for example, the use of 3 molof S (n=1 and x−1=3) per mole of M₂S gives the alkali metal tetrasulfideof formula (X) where x=4.

To return from this to the implementation of step (c), this latter stepis carried out in a wide range of temperatures, ranging preferably from50° C. to 90° C., operating more preferably in the presence of anorganic solvent and, in that context, making use advantageously of thealcohols referred to above with regard to the conduct of phase (2).

The product M-A, and in particular the halide M-Hal, formed in thecourse of reaction is generally removed at the end of the step by meansfor example of filtration.

The bis(monoorganoxydiorganosilylpropyl) polysulfide of formula (I) thatis formed is obtained with a molar yield of at least 80%, based on thestarting monoorganoxydiorganosilylpropyl derivative of formula (IX).

The examples which follow illustrate the present invention withoutlimiting its scope; reference will be made to the attached drawing, inwhich the single FIGURE represents diagrammatically the reactionapparatus including a column which is used in said examples.

In the single FIGURE it can be seen that the apparatus 1 comprises atits base a boiler 2 and a column 3 with a diameter of 40 mm, comprisinga lower part 4 including the foot of the column and an upper part 5including the head of the column. The column contains 15 plates labeled1 to 15. The plates are made of perforated glass. The column 3 isequipped with an ethanol feed tank 6, which feeds the boiler 2 andcertain plates of the bottom part 4 of the column, and also with aliquid recovery tank 7. The column 3 is equipped with a second feed tank8 for optional feeding with liquid ethanol, which allows some of theplates in the upper part 5 of the column 3 to be fed, in order tosimulate a purified ethanol reflux. The column 3 has an ethanol recoverytank 9 which constitutes the distillate and a starting silane feed tank10. The silane is introduced onto a plate in the upper part 5 of thecolumn, and the ethanol in the lower part. The upper part 5 of thecolumn is surmounted by a condenser 11 connected via the pipeline 12 tothe HCl suppression column 13 (HCl trap).

EXAMPLE 1

This example describes the preparation ofbis(monoethoxydimethylsilylpropyl) tetrasulfide of formula (III) inwhich the number x is centered on 4. The reaction scheme concerned bythis example is the following one:

in which the reactant 6 is obtained according to the following equation:

1) Step (a): Synthesis of 3:

A 1 liter stirred glass reactor equipped with a jacket and a stirrer andsurmounted by a distillation column is charged with 165 g of allylchloride 2 with a purity of 97.5% by weight (2.10 mol) and 0.229 g ofcatalyst [Ir(COD)Cl]₂ where COD=1,5-cyclooctadiene and the mixture isstirred in order to dissolve the catalyst completely. The temperature ofthe mixture is adjusted to 20° C. using the heat-exchange fluidcirculating in the jacket.

Dimethylhydrochlorosilane 1, with a purity of 99% by weight, isintroduced into the reaction mixture via a dip tube, using a pump: 196.5g (2.06 mol) of 1 are introduced over 2 hours 35 minutes. The flow rateof introduction is adjusted in order to maintain the temperature of thereaction mixture at between 20 and 25° C., taking into account thestrongly exothermic nature of the reaction. The reaction mixture is keptwith stirring for 20 minutes after the end of the introduction of thedimethylhydrochlorosilane 1.

At the end of the stirring time a sample is taken for analysis. Theresults are as follows: degree of conversion of thedimethylhydrochlorosilane 1=99.8%, and selectivity forchloropropyldimethylchlorosilane 3=92.7% (by analysis by gaschromatography).

The reaction mixture is subsequently distilled under vacuum(approximately 35×10² Pa) at approximately 40° C. to give two mainfractions: ∈ the light products (residual allyl chloride 2 and residualtraces of dimethylhydrochlorosilane 1, accompanied essentially bychloropropyldimethylchlorosilane 3; ∉ chloropropyldimethylchlorosilane3, with a molar purity of more than 98%. A distillation residueconsisting of heavier products, and catalyst, then remains. Molar yield:85%.

2) Step (b): Synthesis of 5:

As indicated above, a column as shown in the single FIGURE is used.

Chloropropyldimethylchlorosilane, stored in the feed tank 10, andethanol, stored in the feed tanks 1 and 3, are injected directly intocolumn 1, at plates 13 and 3 respectively. The column 1 is charged withan appropriate inert solvent, in the present case toluene. The functionof the solvent is to strip the hydrochloric acid (HCl) by mechanicalentrainment, the ethanol also being entrained and optionally recycledafter purification. The solvent also creates a depletion zone (no HCl orvery little in the lower part of the column), thereby making it possibleto restrict the incidence of parasitic chemical reactions.

Toluene is brought to boiling in the boiler (2) by means of electricalresistors. This startup phase takes place with total reflux of thecolumn in order to charge the plates of the column. Thereafter thereflux rate is regulated by a valve situated between the condenser (6)and the distillate recovery tank (4) but not shown in the single FIGURE.

The ethanol is injected into the column in liquid or vapor phase atplate 3 of the lower part 4 of the column. The ethanol flow rate is 100g/h. The chloropropyldimethylchlorosilane is injected at plate 13 inliquid phase, with a flow rate of 120 g/h. The EtOH: silane molar ratiois 3.17.

The ethanol vaporizes in the column and, during its ascension, meets thechloropropyldimethylchlorosilane in liquid phase which is descendingtoward the boiler. The experiment lasts for 5 hours and the overalldegree of conversion of chloropropyldimethylchlorosilane tochloropropyldimethylethoxysilane is from 92% to 94% with a selectivityof more than 90%.

3) Step (c): Synthesis of 7:

3.1) Preparation of Anhydrous Na₂S₄ 6:

-   -   Phase 1: drying of Na₂S hydrate:

43.6 g of industrial Na₂S hydrate flakes containing approximately 60.5%by weight of Na₂S are introduced into the 1-liter round-bottomed glassflask of a rotary evaporator. The flask is placed under an argonatmosphere and then under reduced pressure at 13.3×10² Pa.

The flask is immersed in an oil bath, whose temperature is then broughtto 76° C. This temperature is maintained for 2 hours. Subsequently aprotocol for increasing the temperature of the oil bath is applied inorder to avoid melting the Na₂S, which occurs between 85 and 90° C.approximately. The purpose of the gradual increase in temperature is toaccompany the change in the melting temperature of the product to bedried, which increases when the product undergoes dehydration. Theprotocol applied is as follows: 1 hour at 82° C., 2 hours at 85° C., 1hour at 95° C., 1 hour at 115° C. and finally 1 hour at 130° C. Itshould be noted that this protocol can be odified according to theamount to be dried, the operating pressure and other parameterseffecting the rate at which the water is removed. The amount of waterremoved, measured by mass difference, is 17.2 g, corresponding to amoisture content of 39.5% by weight.

-   -   Phase 2: synthesis of Na₂S₄ 6:

The Na₂S (26 g) dried according to the protocol described above isplaced in suspension in 400 ml of anhydrous ethanol and transferred bysuction into a stirred, jacketed, one-liter glass reactor equipped witha condenser with a possibility for reflux. 31.9 g of sulfur and also 200ml of anhydrous ethanol are additionally introduced into this reactor.The temperature of the mixture is brought to approximately 80° C.(slight boiling of the ethanol) and the mixture is stirred at 600 rpm.The mixture is held at 80° C. for 2 hours. Gradually the solids (Na₂Sand sulfur) disappear and the mixture changes from yellow to orange,then to brown. At the end of reaction the mixture is homogeneous at 80°C.; this gives approximately 58 g of anhydrous Na₂S₄ (0.33 mol) in 600ml of ethanol.

3.2) Preparation of 7:

114 g of chloropropyldimethylethoxysilane 5 with a molar purity of 96.6%(i.e., 0.61 mol) are introduced via a dip tube, using a pump, into theanhydrous Na₂S₄ in 600 ml of ethanol, prepared above, which ismaintained in its preparation reactor at 80° C. (slight boiling of theethanol) and stirred at 600 rpm. A sodium chloride precipitate appears.When the introduction of chloropropyldimethylethoxysilane 5 is at anend, the mixture is held at 80° C. for 2 hours. Subsequently the mixtureis cooled to room temperature, withdrawn and then filtered to remove thesuspended solids, including the sodium chloride. The filtercake iswashed with ethanol in order to extract as much as possible of theorganic products from it. The filtrate is reintroduced into the reactorin order to be distilled therein under reduced pressure (approximately20×10² Pa) for the purpose of removing the ethanol and any lightproducts. 114 g of residue are recovered, which corresponds tobis(monoethoxydimethylsilylpropyl) tetrasulfide, assayed at a purity of97% (molar).

This gives a mass yield of bis(monoethoxydimethylsilylpropyl)tetrasulfide of 87%.

Checking by ¹H NMR, by ²⁹Si NMR and ¹³C NMR makes it possible to verifythat the structure obtained is in accordance with the formula (III)given in the description.

The average number of S atoms per molecule of formula (III) is 3.9±0.1(x=3.9±0.1).

EXAMPLES 2 to 8

Step b) of example 1 is carried out again with the exception that thesites at which the alcohol is injected into the column, and/or theEtOH/silane molar ratio, and/or the reflux rate are modified. Theresults obtained are collated in Table 1 below, where DC and RTrepresent respectively the degree of conversion ofchloropropyldimethylchlorosilane and the selectivity forchloropropyldimethylethoxysilane:

TABLE 1 Plate of Plate of EtOH/silane EtOH silane molar Reflux Exampleinjection injection ratio DC RT rate 1 12 13 1.2 20 88 0.5 2 12 13 3 7093 0.5 3 12 13 6 68 91 0.5 4 3 13 1.2 35 89 0.5 5 3 13 3 92 91 0.5 6 313 6 91 91 0.5 7 3 13 10 89 90 0.5 8 3 13 3 93.5 86 1

From table 1 it emerges that it is preferable to have an EtOH/silanemolar ratio of more than 3 in order to ensure that DC and RT values ofmore than 90 are obtained.

It is also apparent that it is preferable to inject EtOH onto plate 3rather than onto plate 12. In this latter case the reaction volume isinadequate.

Another parameter is the reflux rate. This reflux rate controls thetemperature level in the column but in particular in the amount of HCl(dissolved in the ethanol). And it is this acid which activatesparasitic chemical reactions: example 8 is carried out with a refluxtwice as great as in example 5, and, with all other things being equal,leads to a slight increase in the yield but to the detriment of theselectivity (86% and 91% respectively for examples 8 and 5).

EXAMPLE 9

A continuous reaction is carried out in the same column as for thepreceding examples but without inert solvent. On this occasion theboiler (2) is charged with ethanol (1200 ml). The column (1) is chargedby bringing the ethanol in the boiler (2) to boiling and by working attotal reflux. When the steady-state regime has been attained the refluxis regulated and the 3-chloropropyldimethylchlorosilane is injected ontoplate 13.

The ethanol flow rate (gas phase) is controlled by keeping the level inthe boiler constant. The ethanol flow rate is 500 g/h and thechloropropyldimethylchlorosilane flow rate is 150 g/h, giving anEtOH:silane molar ratio of 12. The yield of the reaction is 100%irrespective of the reflux rate. Conversely the selectivity is afunction of this reflux rate: from 50% for a reflux of 750 g/h to morethan 85% for a zero reflux. It should be noted that in the column used,even at zero reflex, a fraction of the ethanol is condensed directly inthe column. This can be avoided by introducingchloropropyldimethylchlorosilane preheated to 80° C. beforehand in orderto prevent the cooling of the ethanol and its condensation.

EXAMPLE 10

Same experiment as example 3 with introduction of thechloropropyldimethylchlorosilane at plate 7. The results are identicalto the preceding example: DC 100% and RT>85%.

1. A continuous process for preparing an organodialkylalkoxysilane offormula (IX):R¹O—(R²R³)Si—(CH₂)₃—A Comprising the steps of: a) continuouslycontacting an alcohol of formula (VIII): R¹—OH in countercurrent with asilane of formula (VII): Hal-(R²R³)Si—(CH₂)₃—A, in order to carry outthe alcoholysis reaction of said silane in order to obtain the silane offormula (IX) and a product of formula H-Hal, the operation being carriedout with stripping of the product of formula H-Hal formed, and b)recovering the organodialkylalkoxysilane formed in the reactor, in whichformulae the symbol Hal represents a halogen atom selected fromchlorine, bromine and iodine atoms, the chlorine atom being preferred;the symbols R¹, which are identical or different, each represent amonovalent hydrocarbon group selected from a linear or branched alkylradical having 1 to 15 carbon atoms and a linear or branched alkoxyalkylradical having 2 to 8 carbon atoms; the symbols R² and R³, which areidentical or different, each represent a monovalent hydrocarbon groupselected from a linear or branched alkyl radical having 1 to 6 carbonatoms and a phenyl radical; and A represents a removable group selectedalternatively from: a halogen atom Hal belonging to chlorine, bromineand iodine atoms, or a radical para-R⁰—C₆R₄—SO₂—O— wherein R⁰ is alinear or branched C1-C4 alkyl radical, or a radical R⁰—SO₂—O— whereinR⁰ is as defined above, or a radical R⁰—CO—O— wherein R⁰ is as definedabove.
 2. The process according to claim 1, wherein within the reactor adescending liquid fluid comprising the silane of formula (VII) and anascending gaseous fluid comprising the alcohol of formula (VIII) willcirculate in countercurrent.
 3. The process according to claim 1,wherein the alcoholysis reaction is carried out within the reactor at atemperature between the boiling temperature of the alkanol of formula(VIII) and the boiling temperature of the starting silane of formula(VII), the reaction being carried out in the reactor alternatively atatmospheric pressure or at reduced pressure or at superatmosphericpressure.
 4. The process according to claim 1, wherein the silane offormula (VII) is 3-chloropropyldimethylchlorosilane, Hal and A arechlorine and the alcohol of formula (VIII) is ethanol.
 5. The processaccording to claim 4, wherein the 3-chloropropyldimethylchlorosilane, isintroduced in the upper part of the reactor, the ethanol in the lowerpart, the reaction temperature in the column is greater than 77.80° C.and less than 178° C. at atmospheric pressure and the hydrochloric acidformed is stripped by the ethanol.
 6. The process according to claim 1,wherein the reaction is carried out in the presence of an organicsolvent or an inert gas, said solvent having a boiling temperature atthe operating pressure which is between the boiling temperature of theethanol of formula (VIII) and that of the silane of the formula (VII).7. The process according to claim 6, wherein the solvent is toluene,monochlorobenzene or xylene and the products corresponding to formulae(I) to (XI) have ethyl groups R¹ and methyl groups R² and R³ and A andHal represent a chlorine atom.
 8. The process according to claim 1,wherein the pressure inside the reactor is less than atmosphericpressure, atmospheric pressure or greater than atmospheric pressure. 9.The process according to claim 1, wherein the alcohol/silane molar ratiois greater than
 1. 10. The process according to claim 1, wherein thecountercurrent reactor consists of a column equipped in its internalstructure with a dumped or ordered packing or with plates.